Electric discharge device



July 22, 1947. w c w n-E 2,424,526

' ELECTRIC DISCHARGE DEVICE I I Filed Jan. 11 194s Fig.1.

ELECTRON EMISSIVE MATRIAL Inventor: William C.White,

His Atto+-fieg.

Patented July 22, 1947 ELECTRIC DISCHARGE DEVICE William C; White, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application January '11, 1943, Serial No. 471,929

12 Claims.

My invention relates to electric discharge devices and more particularly to new and improved apparatus and methods for energizing cathodes of electric discharge devices.

Due to the precision of control attainable by electric discharge devices, such as those of the controlled type comprising a grid or equivalent member for establishing the electric discharge between an anode and an associated cathode, it is desirable to employ these devices in many fields of application even though the device itself under the conditions imposed may not enjoy an appreciable life.

In accordanc with the teachings of my invention described hereinafter, I provide a new'and improved electric discharge'device, and more particularly a discharge device peculiarly adaptable to those fields of application where, after the intended control function is accomplished, the device itself may be destroyed. In many such applications, due to the limitations placed on the available space for the discharge device itself and the stringent restrictions on the amount of space available for auxiliary equipment such as sources of cathode heating current, I have found the prior art types of electric discharge devices and conventional arrangements for heating a thermionic cathode thereof undesirable or prohibitive.

It is an object of my invention to provide a new and improved electric dischargetdevi'ce- It is another object of my 'inventioni'toiprovide anew and improved cathode heatingstructure for an electricdischarge device.

Itisa'further object of my -invention' to' provide a-new and improved method of heating a therm ionic 'cathode of an electric dischargeflevice. i

It is astill further object'of my invention to provide a new and improved electric discharge device of relatively'smallproportions wherein the hcatifor raising the temperature of an associated thermionic cathode is provided byan externally insertablem'ember'which contains a heatxproduciiig material such as a chemical reactionfimixture.

It is a still further object of my inventionto provide a :new :and improved electric discharge device comprising 'a reentrant part constituting, at least in part, a metallic thermionic cathode and zproviding an externally accessible space. within which a cartridge like metallic member may be readily inserted for the purpose of supp'lying heat to the thermionic cathode.

Briefly stated, inthe illustrated embodiment of my invention I p'rovide a new and imp'roved elec 'tric discharge device which may be peculiarly adaptedifor performing a control'operation and in which the configuration and dimensions of the discharge device arersuc'h that the operation is performed with the desired degree of precision Without entailing "the use of electrical supply equipment or sources of cathode heating current which would otherwise be placed beyond the confines of the envelope constituting a part of the electric discharge device.

One instance of the type of application to which my invention may be applied is that in which-the discharge device is employed for the ignition of an explosive or demolition charge in which instance, inasmuch as the discharge device is usually located within a shell containing the explosive material or in proximity thereto, the discharge device necessarily is destroyed. Consequently, in accordance with one aspect of my invention I provide an electric discharge device in which the period of time within which the cathode is maintained at an electron emissive temperature is relatively short as, for example, in the order of a minute or less.

Fora better understanding of my invention, reference may be had tothe following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. Fig. 1 diagrammatically illustrates an embodiment ofmy invention as applied to an electric discharge device of the triode type, and Fig." 2 diagrammatically illustrates one form of the unitary, externally insertable structure within which the heat producing reaction mixture for the cathode is placed.

In Fig. 1 of the accompanying drawing, there is illustrated an embodiment of my invention as applied to an electric discharge device including an evacuated envelope I which may be constructed substantially entirely of metal. The envelope I may be cylindrical containing a reentrantpart 2, preferably of cylindrical configuration, andcomprises a metallic end part 3 which not only serves as a cathode structure but also serves aspart of the sealing structure of the envelope I. The end part 3 is constructed of a material and designed to have a thickness so that it offers a low thermal resistance to facilitate the raising of the cathode temperature to a value which will sustain an appreciable electric discharge-between a thermionic cathode constituting surface 4 and an anode 5. Cathode surface 4 may be'coated with a suitable electron emissive material, such as an alkaline earth metal or oxide thereof. The entire cathode construction is arranged so that sufficient mechanical rigidity is afforded, thereby maintaining the desired spacing between the electrodes of the discharg device.

Anode 5 may be constructed of a solid piece 7 of metal if desired, and is provided with an exter- I may employ a grid 8 in spaced relation between the cathode surface 4 and anode 5. Grid 8 may be rigidly supported in spaced relation between these electrodes by means of a lead-in conductor 9 supported by a glass bead seal Ill.

The reentrant part 2 of the envelope l provides a cylindrical space which is externally ac-J cessible and into which a member may be, readily inserted for the purpose of supplying heat to the cathode and more specifically to the metal end part 3. I provide a unitary or self-contained cartridge-like member ll, preferably constructed of metal, and which contains a heat producing material such as a reaction mixture for supplying sufiicient heat to the cathode to raise the temperature thereof to a value which will produce appreciable electron emission, or sustain an appreciable electric discharge between the anode and the cathode for a predetermined interval of time commensurate with the intended function of the discharge device as a whole. The cartridge-like member I I may also be of cylindrical form to fafacilitate insertion within the reentrant part 2, and is preferably arranged to engage relatively closely the opposing surface of part 2 and end part 3 so that it is firmly held in the position indicated in Fig. 1.

In Fig. 2 there is shown in cross section the uni tary or self-contained cartridge-like member H which is illustrated as comprising a metallic wall member l2 having an end part I 3 of relatively low thermal resistance to facilitate transmission of the heat incident to the reduction of the rea tion mixture to the end wall 3 shown in Fig. 1. The character and quantity of the reaction mixture are suitable for producing the requisite amount of heat during the time desired. The reaction mixture is preferably of the nonexplosive type so that the rate of rise of the temperature of the electron emissive surface may be'readily controlled. An example of one type of a chemical reaction mixture which may be employed is a mixture of aluminum powder and ferric oxide, commonly termed thermite. One end of member ll may be closed by means of 'a. cap 14 provided with a screw thread to engage wall member l2.

Within the unitary member I I, I provide ignition means for initiating the heat producing operation of the reaction mixture at the desired time. This means may assume a variety of forms, such as an ignition cap, or a rapidly oxidizable metal such as a strip of magnesium, indicated by the reference numeral l5, which is placed within or in close proximity to the reaction mixture. For the purpose of controlling the time of ignition, I provide a pair of lead-in conductors l6 and H which are electrically insulated from cap [4 by glass beads l 8 and I9, and which serve as electrical conductors for supplying electric current to the ribbon IS.

The ignition means, which may comprise an oxidizable strip of metal such as the strip 15 of magnesium, is preferably located within the vicinity of the end of the self-contained member adjacent the electron emissive surface or cathode, so that great precision in the control of the cathode temperature and the rate of rise of the cathode temperature are obtainable. For example, the ignition means may be located as illustrated within the vicinity of the end part I3.

One of the important advantages afforded by the embodiment of my invention illustrated is the conservation in space required for the electric discharge device and elimination of the conventional externally spaced means for supplying cathode heating current. This advantage is obtained primarily by virtue of the reentrant part of the envelope which not only substantially encloses and holds the metallic container for the reaction mixture, but also places it in a position whereby the overall configuration of the discharge device is simple and readily adaptable to manipulation and handling.

A further advantage is the simplicity of construction whereby the conventional filamentary heating element for supplying heat to the cathode is eliminated.

The above advantages are attained without sacrificing precision of control of the discharge device inasmuch as the enclosing envelope 1 and reentrant part 2 are constructed to have sufficient rigidity to maintain the electrodes firmly in position even though subjected to appreciable sho :k.

In the operation of the electric discharge device, it will be appreciated that the time of initiation of current flow between the anode 5 and cathode 4 may be obtained by impressing a suitable potential on the grid 8. For example, the potential of grid 8 may be normally maintained negative with respect to the cathode to prevent conduction of current between the anode and cathode until a desired time. The initiation of current fiow between the anode and cathode may be obtained by any conventional arrangement whereby the potential of the grid with respect to the cathode is raised.

One sequence of operation in the use of the above described electric discharge device may comprise the insertion of the self-contained member or capsule I2 into the recess provided by the reentrant part 2; maintenance of a negative or suitable voltage on grid 8 to prevent anodecathode current conduction until a desired time; ignition of the reaction mixture by the transmission of current through conductors l6 and i! thereby raising the temperature of the cathode to an electron emissive value; and lastly the initiation of current flow between the anode and cathode by raising the potential of the grid 8.

A second method in the sequence of operation of the above described electric discharge device may comprise the insertion of the self-contained member or capsule l2 into the recess provided by the reentrant part 2 and ignition of the reaction mixture by the transmission of current through conductors l6 and I1, thereby raising the temperature of the cathode to an electron emission value and utilizing the rate of rise of the cathode temperature to control the time of initiation of current flow between anode 5 and cathode surface 4. According to this method of operation, the time of initiation of current conduction is controlled solely or principally by the cathode temperature.

Alternative forms of construction of the selfcontained member l2 will, of course, be apparent depending upon the nature of the chemical reaction mixture which is employed for heating the cathode emissive surface. For exampe, if it is desirable to use a reaction mixture which produces a temperature approximating or exceeding the melting point of the lower melting point metals such as ordinary iron, the self-contained member l2 may be constructed of a refractory material, or may be constructed of metal having a lining of a refractory material, containing the chemical reaction mixture, in which instances the end of the self-contained member l2, that is, the end part l3 may be constructed of a heat resistant or refractory metal such as molybdenum.

While I have shown and described my invention as applied to an electric discharge device of a particular type, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric discharge device, the combination comprising a plurality of enclosed electrodes and having a metallic part constituting a cathode, said metallic part being provided with an electron emissive material, and a self-contained member totally enclosing a reaction mixture for heating said cathode.

2. In an electric discharge device, the combination comprising an envelope enclosing a plurality of electrodes including a thermionic cathode and comprising a metallic part of relatively low thermal resistance, and a unitary receptacle adjacent said metallic part and totally enclosing a heat producing reaction mixture.

3. In an electric discharge device, the combination comprising an envelope enclosing an anode and a thermionic cathode, said cathode comprising metallic structure of low thermal resistance and formed to receive a metallic capsule, and a metallic capsule containing a heat producing reaction mixture positioned in said structure.

4. In an electric discharge device, the combination comprising a plurality of electrodes, an envelope enclosing said electrodes and comprising a reentrant part having a metallic member constituting a cathode, and means for supplying heat to said cathode comprising a cartridge-type member containing a heat producing reaction mixture and adapted to be inserted within an externally accessible space provided by said reentrant part.

5. In an electric discharge device, the cornbination comprising a plurality of enclosed electrodes, a cylindrical metallic envelope having a reentrant part providing an externally accessible space, one part of said reentrant part comprising a. cathode, insulating means supporting said anode in spaced relation with respect to said cathode, and means for supplying heat to said cathode comprising a unitary member in juxtaposition to said cathode and containing a reaction mixture.

6. In an electric discharge device, the combination comprising a plurality of enclosed electrodes including an anode and a thermionic cathode, said envelope being formed to provide a reentrant portion and having on a surface thereof facing said anode an electron emissive material, and a unitary metallic capsule containing a heat producing reaction mixture and insertable within the space provided by said reentrant portion.

7. In an electric discharge device, the combination comprising an anode, a, cathode and a grid in spaced relation between said anode and said cathode, said cathode comprising a metallic supporting structure having an electron emissive surface facing said anode, an envelope enclosing the electrodes and supporting said cathode structure, and a unitary metallic structure in juxtaposition to said cathode structure and containing a, reaction mixture for raising the temperature of said cathode to a value sufiicient to sustain an appreciable electric discharge between said anode and said cathode.

8. In an electric discharge device, the combination comprising an anode, a cathode and a grid in spaced relation between said anode and said cathode, said cathode comprising a metallic supporting structure having an electron emissive surface facing said anode, an envelope enclosing the electrodes and. supporting said cathode structure, and a unitary metallic cartridge containing a reaction mixture to raise the temperature of said cathode to a value sufficient to sustain an appreciable electric discharge between said anode and said cathode for a predetermined interval of time.

9. The method of supplying heat to a thermionic cathode of an electric discharge device which comprises placing a reaction mixture in proximity to the cathode and igniting the mixture.

10. The method of controlling an electric discharge device comprising an anode, a thermionic cathode and a control grid which comprises placing a chemical reactive mixture in proximity to the cathode, igniting the mixture to supply heat to the cathode to raise the temperature thereof to a value to effect substantial electron emission therefrom, and controlling the potential of the grid.

11. The method of controlling an electric discharge device comprising an anode and a thermionic cathode which comprises placing a chemical reaction mixture in proximity to the cathode, igniting the mixture to supply heat to the oathode to raise the temperature thereof to a value to eiiect substantial electron emission therefrom and utilizing the rate of rise of the cathode temperature to control the time of initiation of current flow between said anode and said cathode.

12. In an electric discharge device, a thermionic cathode, a heat producing device for said cathode including a metallic container having a portion thereof positioned adjacent said cathode, a heat producing reaction mixture enclosed in said container, and means for igniting said mixture.

WILLIAM C. WHITE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,965,849 McIlvane July 10, 1934 1,886,705 Lucian -1 Nov. 8, 1932 1,927,631 Edelman Sept. 19, 1933 1,654,513 Round Dec. 27, 1927 1,673,850 Tietig June 19, 1928 2,114,114 Roberts Apr. 12, 1938 2,125,279 Bieling Aug. 2, 1938 2,167,201 Dallenbach July 25, 1939 FOREIGN PATENTS 0 Number Country Date 236,992- Great Britain July 13, 1925 244,196 Great Britain Dec. 17, 1925 

